This paper describes the process of design, implementation, and real world deployment of a web-based network exploration tool called Network Explorer. We designed Network Explorer based on the expressed needs of our clients and later deployed it as part of a larger system for fraud detection in health care. Our implementation of Network Explorer provides visual interactive access to large-scale network data. As part of the Network Explorer tool we contribute a dynamic group-in-a-box implementation for laying out clusters, and a node navigator widget that aids in the exploration of large networks. We are also contributing two open source components of the Network Explorer for the community to reuse: an in-browser clustering library, and the dynamic group-in-a-box algorithm. We have evaluated the network explorer tool in multiple real-world environments including the fraud detection setting above.

Detection of fraud, waste, and abuse (FWA) is an important yet difficult problem. In this paper, we describe a system to detect suspicious activities in large healthcare claims datasets. Each healthcare dataset is viewed as a heterogeneous network of patients, doctors, pharmacies, and other entities. These networks can be large, with millions of patients, hundreds of thousands of doctors, and tens of thousands of pharmacies, for example. Graph analysis techniques are developed to find suspicious individuals, suspicious relationships between individuals, unusual changes over time, unusual geospatial dispersion, and anomalous networks within the overall graph structure. The system has been deployed on multiple sites and data sets, both government and commercial, to facilitate the work of FWA investigation analysts.

This paper is concerned with the problem of reliably maintaining synchronization in redundant systems. While many such systems have been built, little work has been done on formalizing their requirements. The terms necessary to quantify the problem and general synchronizer specifications are given. To illustrate their use and point out issues in synchronization, a synchronizer is advanced and three detailed examples of its use are given. These are a single fault tolerant clock and a TMR microcomputer system synchronized first predominately with hardware, then with software.

Most of the published work on massive redundancy makes one crucial assumption: the redundant modules are synchronized. There are three ways of achieving synchronization in redundant systems-independent accurate clocks, a common external reference, and mutual feedback. The use of a common external reference is currently the most widely used technique, but suffers from vulnerability to common-point failures. We introduce a novel mutual feedback technique, called "synchronization voting," that does not have this drawback. A practical application of synchronization voting is described in the appendix—a fault-tolerant crystal-controlled clock.